1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to a method for manufacturing a thin-film transistor (TFT) substrate.
2. The Related Arts
Thin-film transistors (TFTs) are widely used in electronic devices as switching devices and driving devices. Specifically, since the thin-film transistors can be formed on a glass substrate or a plastic substrate, they are often used in the fields of flat panel displays including liquid crystal displays (LCDs), organic light-emitting displays (OLEDs), electro-phoretic displays (EPDs).
Oxide semiconductors have a relatively high electron mobility (the electron mobility of oxide semiconductors >10 cm2/Vs, while the mobility of amorphous silicon (a-Si) being only 0.5-0.8 cm2/Vs). Further, the manufacturing process of oxide semiconductors is simple as compared to that of low-temperature poly-silicon and is compatible with that of amorphous silicon, allowing it to be applied to various fields including liquid crystal displays, organic light-emitting displays, and flexible displays and compatible with high generation manufacturing lines to be applicable to large-, medium-, and small-sized displays, having a prosperous future of application and being a hot spot of current researches.
Heretofore, the commonly seen oxide semiconductor thin-film transistors include: etch stopper based oxide semiconductor thin-film transistor and back channel etching based oxide semiconductor thin-film transistor.
Referring to FIG. 1, which is a schematic view showing the structure of a conventional etch stopper based oxide semiconductor thin-film transistor, an etch stopper layer (ESL) 300 is formed after an oxide semiconductor layer 100 is formed but before a metal source/drain electrode 200 is formed to protect the oxide semiconductor layer 100 in a back channel from damage caused in the subsequent processes (such as processes including etching of the metal source/drain electrode 200 and exposure of passivation layer 500) so as to enhance stability of the oxide semiconductor thin-film transistor. However, additionally making the etch stopper layer requires an additional photolithographic process and a photolithographic process includes steps of film formation, exposure, development, etching, and peeling. Thus, additionally making an etch stopper layer would greatly increase the manufacturing cost and lower yield rate.
To cope with these problems, a back channel etching based oxide semiconductor thin-film transistor omits the etch stopper layer formed on the oxide semiconductor layer in order to reduce the photolithographic processes and lower down the manufacturing cost.
Referring to FIG. 2, which is a schematic view showing the structure of a conventional back channel etching based oxide semiconductor thin-film transistor, after an oxide semiconductor layer 100′ is formed, a metal source/drain electrode 200′ is directly formed thereon and then a passivation layer 500′ is formed on the metal source/drain electrode 200′.
Such a back channel etching based oxide semiconductor thin-film transistor, although having a simple structure and manufacturing process and having a relatively large channel width/length (W/L) ratio, the etching process of the metal source/drain electrode 200′ often uses strong acids and mixtures thereof (such as HNO3/H3PO4/CH3COOH) as etchants. This readily leads to damages of the oxide semiconductor layer 100′ in the back channel and deterioration and instability of the oxide semiconductor thin-film transistor may result.